Late '66 to early '67 Transistion to EL34's, steel chassis and gold rear panel. Earliest JMP's.

Still 2" Drake OT, the 1202-119 (8,16 and 100V taps) or 1202-132 (4,8,16). Both with 1.7k primary. Sometime in '66 the Drake 1203-80 voltage doubler PT came in to use. More research needed on PT's.
Filtering now is 100,100, 32,32, 32 (mounted on chassis), 16,16 (on board).
470k mix resistors. 56k/250pf tone stack. .1uf PI caps.

Mid to late '67 Change to Dagnall 1.5" OT's.

Most other specs the same for a transitional time peroid leading up to the 12000 series.

Very late '67 to early '68. The 12000 series plexis. Named for the serial #'s in the 12xxx range. EVH's famous amp is from this era.

Now we see the first split cathodes using a 820/.68uf combination. Normally with a 820/.68uf in V2 as well. The Tone stack changes to the 33k/500pf arrangement. 47k NF. .022uf PI caps. .0022uf cap in the bright channel V1.

Late '68 to July '69

All filter caps now mounted on top of chassis. The .68uf cap in V2 shows up intermitantly. And the 2.7k replaces the 820 in the split cathode on V1.
47k NF resistor.
Filtering is now all dual 50uf cans.

July '69 The metal panel era begins.

George,

what was the advantage of the filter caps changing from 100,100, 32,32,32/ to 50uf cans?

Late '66 to early '67 Transistion to EL34's, steel chassis and gold rear panel. Earliest JMP's.

Still 2" Drake OT, the 1202-119 (8,16 and 100V taps) or 1202-132 (4,8,16). Both with 1.7k primary. Sometime in '66 the Drake 1203-80 voltage doubler PT came in to use. More research needed on PT's.
Filtering now is 100,100, 32,32, 32 (mounted on chassis), 16,16 (on board).
470k mix resistors. 56k/250pf tone stack. .1uf PI caps.

Mid to late '67 Change to Dagnall 1.5" OT's.

Most other specs the same for a transitional time peroid leading up to the 12000 series.

Very late '67 to early '68. The 12000 series plexis. Named for the serial #'s in the 12xxx range. EVH's famous amp is from this era.

Now we see the first split cathodes using a 820/.68uf combination. Normally with a 820/.68uf in V2 as well. The Tone stack changes to the 33k/500pf arrangement. 47k NF. .022uf PI caps. .0022uf cap in the bright channel V1.

Late '68 to July '69

All filter caps now mounted on top of chassis. The .68uf cap in V2 shows up intermitantly. And the 2.7k replaces the 820 in the split cathode on V1.
47k NF resistor.
Filtering is now all dual 50uf cans.

July '69 The metal panel era begins.

George,

This may take some time, but is it possible to explain after Marshall started making these changes what effect each change was having on the amps?

I have two 100w, and two 50w Plexis. I don't belive in using the mustards to date an amp. I have a JTM100 dual OT Super PA, and I think we can agree that the amp was built late '65. The mustards date D3 and B4 on that amp. The only thing it tells me is that the amp was made after the second quarter of '64. And we all know that this amp was made over a year after that.

I also have a very early JMP 50w with steel chassis and a tuberectifier that I belive is from late -67. The mustards on this amp is dated B6 exept for the two bigger ones that are dated B7.

Some of the information in Doyles book has to be wrong. My JMP 50w is almost two years older than my JTM100, and still has the tuberectifier. Doyle says it disappeared from the 50w a few months later when the 100w was introduced without a tuberectifier.

I belive both amps to be very close to original, and they have never been in the hands of a vintage dealer.
Here's some pictures of my very early '65 JTM100 Super PA

Flipping heck!!
That is the wierdest thread I've read in a while!
Mr G? Guest?
All credit to these people really. But this subject appears to be about history rather than tone.
I suppose it is very, very important to have your facts straight if you want to lay claim to having the most accurate vintage Marshall replicas.

Personally, I always think history needs to be constantly reviewed to ensure it's accuracy, but as far as buying an amp goes, I'm not too fussed about it, as long as it looks the part, is built from quality bits and sounds gorgeous.

GEORGE,
I now own a 1972 HW amp
1977 PCB 100w amp
and a 1981 JCM800 2203

I find special things in each amp. Being formulaic of course i run the least amount of outboard gear with these amps leting the amps themselves do the talking . The "FORMULA" itself are the components you surround your amo with which gives you the end result always .

I FIND this most prevelant in your 1968 12000 series YOUTUBE VIDEO. YOUR using Blackback cab with simply ROLA G12m25 speakrs and it sounds UN BELIEVABLE> TRuly unBELIEVEABLE. I thought after the early 70s or around then afterthey ravaged the laws about what WAS and what WAS NNOT ALLOWED INSIDE A TRANSFORMER , A CHOKE ,etc. i.e asbstos, lead,etc. I thought. Thats it , That must be why people just thrive on buying these old amps . Not true !

Im sure there is a small amount to do with overall tone with having certain ingrediant in a main piece of gear inside your head . But closing your eyes and just listening with some good head phons to not just the 68 but all your amps you really are the ONLY cat know that just doent ever STOP

I will be in touch As I save money I do want the 68'

Let me knoe your thoughts if poddible in a PM MESSAGE about the differnae in H.W to PCB in the 60,70s, and 81 to 83 before Mrshall started to , umm lets say , start to cut covers ?

Thanks George
________________________________________________________________________

Georges info CONTNUED:->

quote="VelvetGeorge"]A work in progress.

In order to trace the evolution of the superlead circuit, and to help us communicate about the different eras. I'll try to chronical it here.
I'll update the info as I have it.

Late '66 to early '67 Transistion to EL34's, steel chassis and gold rear panel. Earliest JMP's.

Still 2" Drake OT, the 1202-119 (8,16 and 100V taps) or 1202-132 (4,8,16). Both with 1.7k primary. Sometime in '66 the Drake 1203-80 voltage doubler PT came in to use. More research needed on PT's.
Filtering now is 100,100, 32,32, 32 (mounted on chassis), 16,16 (on board).
470k mix resistors. 56k/250pf tone stack. .1uf PI caps.

Mid to late '67 Change to Dagnall 1.5" OT's.

Most other specs the same for a transitional time peroid leading up to the 12000 series.

Very late '67 to early '68. The 12000 series plexis. Named for the serial #'s in the 12xxx range. EVH's famous amp is from this era.

Now we see the first split cathodes using a 820/.68uf combination. Normally with a 820/.68uf in V2 as well. The Tone stack changes to the 33k/500pf arrangement. 47k NF. .022uf PI caps. .0022uf cap in the bright channel V1.

Late '68 to July '69

All filter caps now mounted on top of chassis. The .68uf cap in V2 shows up intermitantly. And the 2.7k replaces the 820 in the split cathode on V1.
47k NF resistor.
Filtering is now all dual 50uf cans.

Just wanted to tell you briefly i now have three Marshall amps and have had a new ffiend of mine build me a four space amp head . It is great. Their is space for one more head. I have been dialing and dialing in the EQ on the amp and my 1973 Gibson Les Paul. I had Xtra Jumbo frets, the serial number surned in deeper and a minor neck issue spreayed over that had laready been fixed perfectly . IT plays itslelf now
I needed this last amp and guitar worked on becasue of some work coming up for me finally. I am really psyched.
I WANT TO KNOW HOW you can sustain a 68 12000 100 watt amp. ( I have a 1977 Marshall G12M25 Blackback 4x12" half stack cab for it ) or long periods of time using
attenuation .

you can OM me with the info
MAIN uestions.
1.
Just want to know. Did you use new productio ntubes in the 69 120000 repro on the youtube 120000 series video? and what werethey if so. Im game for NOS dependant on cost. I have a knock for finding good deals on quality noS tubes . I have Mullard 12ax7s already so thats done . Ill use those
#2
Attenuation I would is the way to go and run it 10s across th bpard for the EVH tone. This is what i want to achieve obviously with the amp.
3Most important.
I THOUGHT i Read where I can buy the kit , ill go with what you think is best i.e , choke ,trnnies ,etc. hoewever is there a deal on after purchasing the kit on where you can build it for a cetain price or farm it out to a reputablr colleqgue or somone in i]your oganization to buld it .they can take there time since ill bre payong in a few installments.
4. Just PM me and well chat more

The Super 100 Amplifier (JTM45/100) and the plexi Superleads (updated 2012): http://folk.ntnu.no/roef/JTM100.html
________________________________________
JTM45/100 is the name of the first 100 watt amps that used the JTM45 plexi facepanels and the white Super 100 Amplifier backpanel. The PA amps had usually JTM100 facepanels and are therefore called JTM100s. The main stages in the evolution of these early 100 watters are:
1. 1965: Prototypes
2. 1965: Dual output transformers (Drakes) and Radiospares Power transformer.
3. 1966: Single output transformer and Drake 1204-43 power transformer.
4. 1967: First EL34 amps with Drake 1202-119 output transformer and aluminium chassis
5. 1967: Second series of EL34 amps with dual rectifiers.
6. 1967: JMP100 facepanels with Drake 1202-132 output transformer, new power supply.
7. 1968: Dagnall output transformer (C1998) and a new Superlead circuit.
8. 1969: New chassis and stiffer filtering
9. 1969: Yet another chassis, standup power transformer (T2562), last plexis.
10. 1969-: Aluminium panel amps
________________________________________

Last edited by Roe on Mon Apr 08, 2013 6:05 am, edited 4 times in total.